[Fix] Fixed an type annotation error: type of OrderRequest.price_type should be PriceType but not string.
[Fix] Fixed an type annotation error: type of OrderRequest.price_type should be PriceType but not string.

bigdig/vnpy,msincenselee/vnpy,andrewchenshx/vnpy,vnpy/vnpy,andrewchenshx/vnpy,andrewchenshx/vnpy,bigdig/vnpy,bigdig/vnpy,vnpy/vnpy,msincenselee/vnpy,andrewchenshx/vnpy,andrewchenshx/vnpy,msincenselee/vnpy,bigdig/vnpy,msincenselee/vnpy